Eugene raised the question of AST changes on python-dev [1] and the verdict was that so long as ast.__version__ is updated, AST clients will be able to cope with changes.
Benjamin Peterson made some subsequent changes to the AST (bringing the AST for try and with statements more in line with the concrete syntax, allowing source-to-source transforms to retain the original code structure).
This patch will probably need to be updated to be based on the latest version of the AST - I would be surprised if it applied cleanly to the current tip.
[1] http://mail.python.org/pipermail/python-dev/2011-April/110399.html